The subject matter of the present invention relates generally to optical copying apparatus for making multiple copies of an optical data record of digital or analog data, and in particular to such a copying apparatus employing a multiple lens array which is scanned across the master record during copying.
The present optical copying apparatus is especially useful for copying a video disc having digital color television signals recorded thereon. Such copying apparatus has the advantage that, unlike contacting record copiers, it does not wear out the master record having original data recorded thereon, and may employ relatively low cost lenses while making copies of high density data records with great accuracy and low distortion. This low image distortion is made possible by supporting the array of lenses and limiting the viewing fields of such lenses so that such fields do not overlap but are spaced apart by field gaps. These field gaps are aligned with data gaps between data groups on the record, so that different data groups are transmitted through each lens of the array. A mask is employed with apertures in alignment with the lenses and may be supported in position between the lenses of each of a plurality of lens pairs forming the array, in order to limit the fields of view of such lens pairs to the central portions of the lenses which is substantially linear and has no magnification distortion.
It has been previously proposed to make optical digital data records by a recording means using a light beam focused on photographic film, as shown in U.S. Pat. No. 3,465,352 of C. O. Carlson, granted Sept. 2, 1969, and U.S. Pat. No. 3,422,219 of L. R. Teeple, granted Jan. 14, 1969. However, previously there has been no satisfactory copying apparatus for making multiple copies of optical records of high density digital or analog data, such as for example would be required for producing consumer television records or high fidelity audio music records. Conventional photographic enlargers were previously employed for copying optical data records and employ a single imaging lens having a wide viewing field. Ordinarily enlarger lenses do not have the high image resolution and field linearity required for copying high density optical data. Thus, digital optical records may have binary information bits on the order of approximately one micron in diameter and the data is stored at extremely high densities on the order of about 10.sup.+8 bits/inch.sup.2. As a result of this extremely high bit density and small bit size, any appreciable lens distortion would prevent accurate copies of the master record from being made.
It is economically unfeasible to use single lens type optical copiers for copying optical records of high density data, due to the high cost of making a suitable lens of high enough quality. In order to overcome this problem, the optical copying apparatus of the present invention employs an array of a plurality of relatively small, inexpensive lenses supported adjacent a mask whose apertures are aligned with such lenses so that only the high resolution, linear central portions of such lenses are employed for image transmission. This mask stops light from being transmitted through the outer portions of the lens adjacent the periphery thereof which are of low linearity and poor image resolution, thereby preventing distortion of the optical image transmitted through such lens. As a result, the useful viewing fields of the lenses do not overlap but are spaced apart by field gaps. The field gaps are aligned with data gaps between adjacent data groups on such record so that such field gaps do not prevent any of the optical data on the master record from being copied as the lens array is scanned across such master record.
Previously it has been proposed to provide an optical copying apparatus for copying analog images, such as document pages, by employing an array of lenses which is either fixed or is scanned across such document, as shown in U.S. Pat. No. 3,584,950 of R. Gundloch, granted June 15, 1971, U.S. Pat. No. 3,592,542 of H. Kaufer et al, granted July 13, 1971, and U.S. Pat. No. 3,605,593 of R. H. Anderson, granted Sept. 20, 1971. However, in all of these office copier types of optical copying apparatus, the viewing fields of the lenses overlap and are free of any gaps between viewing fields in order to provide a continuous image of the document or other object being copied. As a result, such optical copiers are not suitable for copying optical records of high density data because of the distortion caused by the overlapping viewing fields. This distortion would prevent accurate copies of the data record from being made with such prior copying apparatus. For example, the lens distortion in lenses typically used for office copiers is about 1%. This 1% distortion is unnoticeable in copies of the documents. However, it is totally unacceptable when making copies of high density optical data records, such as video records of digital television line signals. A digital television line signal would typically have about 1000 bits per line so that when its image is transmitted through one of the lenses, the 1% error would then amount to 10 bits per line, which is too great for commercial acceptance.
This problem is avoided in the copying apparatus of the present invention by employing field gaps between the viewing fields of the lenses and aligning such gaps with corresponding data gaps between adjacent data groups on the master record. For example, such data gaps may be approximately 250 microns wide and may correspond to the horizontal blanking periods between television line signals which are recorded in a plurality of data tracks on such record so that the data gaps of adjacent tracks are laterally aligned to enable the lens array to scan laterally across such data tracks while the field gaps remain aligned with such data gaps.